I hope my perl script can run faster, however it should not eat up all the CPU resouce.

Why shouldn't it use all the CPU resource? What are you saving it for?

Essentially what I'm saying here is that cpu resource is time; and time inexorably moves forward; you cannot save it for later; so unused CPU is essentially wasted cpu that you can never recover. Your processor should either be running as close to 100% as your workload permits; or it should be idle because you have nothing to do. Trying to restrain it to say 75% or whatever; doesn't achieve anything not even energy savings.

Perhaps what you are concerned with is that you want to ensure that some other, sporadic processes will have an opportunity to run concurrently with this workload when they need to?

If so, the proper way to deal with that is not to try an 'reserve' some cpu; but rather to run this workload at a lower priority than the sporadic workload(s) so that you make full use of the cpu for this workload when can; whilst ensuring that those sporadic workloads will get a look in when they need it.

Hi,

Thanks a lot for your reply. In my environment, many users are sharing hosts, and each job has CPU quota. If you request more quota like occuping the host exclusively, pending time would be longer, so I prefer to limit my CPU quotas to a optimal size.

In my environment, many users are sharing hosts, and each job has CPU quota.

1. Is it a virtualised environment?

   Ie. Is your process running in a VM or container?

2. What units are your CPU quotas specified in?

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It sounds strange that you want to multithread for more speed, but then turn around and want to use less CPU % (so it takes longer again?).

Do you have busy loops wasting CPU cycles or something? If so, use a sleep or a select(undef,undef,undef,0.01 to reduce the polling rate and drop the CPU usage to <1%.

You can try a nap of a few milliseconds per iteration on your big long running loops as well if they're hogging resources, but if the loop is doing productive things, letting it finish is usually a good idea ;).

On a unix box you can play with BSD::Resource (see setpriority()) or play with the nice command.

("nice perl myscript.pl" is a good start..)

Thanks a lot. It's helpful.

taskset -cp 3,4 1234
[download]

taskset -c 1,2 script.pl
[download]

Thanks for the reply.

Not for the faint of heart, but there is a syscall in perl. To hack a sched_setaffinity call, one might:

#! /usr/bin/perl

sub setaffinity {
  use Config;
  die if "@Config{qw(ptrsize archname)}" !~ /8.*x86_64.*linux/;

  my $mask = pack "Q", shift;
  syscall 203, 0, 8, $mask;
}

setaffinity 0x22; # allow cores/threads 1 and 5
fork for 1..3;    # 8 workers
1 while 1;        # busy we are
[download]

To easily find out the linux syscall numbers, I recommend looking at strace sources: there are syscallent.h headers for each architecture.

Thanks for the suggestion!